Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.88   6.395%   $222.2379   $222.24   $222.25   $222.20  
  Purchase #2 $40.25   3.354%   $41.6   $41.60   $41.60   $41.60  
  Purchase #3 $118.83   13.571%   $134.9564   $134.96   $134.95   $135.00  
  Purchase #4 $61.35   5.107%   $64.4831   $64.48   $64.50   $64.50  
  Purchase #5 $209.50   3.621%   $217.086   $217.09   $217.10   $217.10  
  Purchase #6 $179.77   13.724%   $204.4416   $204.44   $204.45   $204.40  
  Purchase #7 $243.88   8.249%   $263.9977   $264.00   $264.00   $264.00  
  7 purchase totals = $1,062.46       $1,148.8027   $1,148.81   $1,148.85   $1,148.80